The applicant seeks support for a midcareer investigator to conduct intensive mouse immunopathology research using comparative pathology approach and to mentor beginning investigators in mouse pathbiology research. Dr. Chen Liu is a board-certified surgical pathologist. He is an Associate Professor, the Director of Gastrointestinal and Liver Pathology Service, and the Director of GI/Liver Pathology Fellowship training program. Dr. Liu is actively engaged in clinical patient care, basic and translational research using mouse models, and mentoring clinical fellows, residents, postdoctoral fellows, graduate students, and undergraduate students. Dr. Liu's primary research focus is immunopathology of hepatitis C viral infection, which is currently supported by NIH grants. His team has established novel mouse models to investigate immune responses in viral infection. In this proposal, he will study the T cell response and the function of regulatory T cells in HCV infection. He will test novel strategies to harness the immune response against HCV infection. Dr. Liu's research group consists of very talented young postdoctoral research fellows, graduate students, residents/follows, medical student, and undergraduate student. The goal is to mentor beginning investigators to become future investigators who have the expertise in both mouse and human immunopathology. In addition, Dr. Liu has established international collaborations on mouse immuopathology research. Through these studies, Dr. Liu has established himself as an expert in comparative mouse immunopathology. Over the past 8 years, Dr. Liu has co-authored 63 peer-reviewed articles and 9 book chapters/reviews. Within the Institution, Dr. Liu is a well-established pathologist who has expertise in both human and mouse systems. He is involved in research projects on autoimmune diseases using mouse models. Because of these extensive ongoing research activities, Dr. Liu intends to have dedicated time to train new investigators who will fill the growing need of mouse pathologist in biomedical research. The University of Florida has a comprehensive animal care facility with 169,026 square feet of space that hosts more than 350 strains of mice and 1,400 approved research protocols. With additional collaborations locally and nationally, the institution will provide an outstanding environment for Dr. Liu's career development and mentoring next generation of mouse pathobiologists. The K26 midcareer award is an excellent mechanism to support Dr. Liu to achieve this goal.